Charting a new process for magnesium alloy formability

Picture Credit: Abhishek Tripathi

One of the biggest causes of global warming is vehicular emissions. Scientists across the world are working to make environmentally friendly fuel, and even engines. But what about simply reengineering the car so that it’s lighter and, therefore, more efficient in burning that fuel?

Cars today are made of aluminium and steel. A cubic metre of aluminium weighs 2,600 kg, and a corresponding volume of rolled steel weighs 7,850 kg. IITB-Monash Research Academy scholar Abhishek Tripathi has turned his attention to magnesium, a strong metal that has the highest strength to weight ratio when compared with steel and aluminum. A cubic metre of magnesium comes in at 1,738 kg.

Picture Credit: Abhishek Tripathi

In the real world, however, magnesium and its alloys remain limited in their application because of its low formability. A material’s ability to be moulded, or its formability, depends on the orientation of its crystals. The main thrust of Tripathi’s research is improving its formability by suitable alloying or by developing novel processing techniques that will improve the microstructure and texture to result in improved formability.

To make it ductile and more pliable, even magnesium alloy has to be improved through some process. “Conventional processing techniques like rolling, forging, extrusion are widely used to improve the mechanical properties of structural alloys, but they are time consuming and have limited microstructural modifications,” said Tripathi. Instead, his work has focused on a novel advanced processing technique called Friction Stir Processing (FSP).

FSP is a short route, solid-state processing technique that can achieve microstructural improvements like refinement, densification, and homogeneity quickly and in a single step.

Picture Credit: Abhishek Tripathi

To imagine how FSP works, think of a large mortar and pestle grinding up a metal sheet, in this case AZ31 magnesium, an alloy so called because it’s three percent aluminium and one percent zinc.

The microstructure and mechanical properties of the processed region can be accurately controlled by optimizing the processing parameters, and these parameters are exactly what Tripathi is monitoring.

“The impetus is not only because of commercial and environmental applications in the automobile industry, the fundamental science of it is also worth exploring,” said Tripathi. Texture analysis in hexagonal close packed metals like magnesium has not been widely studied so far and so there is no clear understanding of it.

Additionally, various theories explaining the mechanisms during the process are being proposed in the scientific community about the microstructural and texture evolution during friction stir processing. Tripathi’s modeling work looks at the effect of multi-pass and multi directional FSP on the microstructure and texture evolution in case of magnesium alloy AZ31. He has also proposed a texture evolution route that can quantitatively explain the experimentally observed texture as well as the thermal history during processing by a finite element model.

Tripathi is conducting his research at the IITB-Monash Research Academy, a pioneering joint-venture research partnership between the leading institutions in India and Australia. The Academy, as it is commonly referred to, offers research scholars the opportunity to study for a dually-badged PhD from both IIT Bombay in India and Monash University in Australia. Students spend time at both countries over the course of their research and many of them work on projects that are strongly interdisciplinary in nature and with an applied research focus. Some day, this could be the basis of a whole new generation of cars.

Research scholar: Abhishek Tripathi, IITB-Monash Research Academy

Project title: Friction Stir Processing of AZ31 Magnesium alloy

Supervisors: Dr. Indradev Samajdar, Dr. Asim Tewari, Dr. Jian Feng Nie.

Contact details: abhishek.tripathi@iitb.ac.in

Contact research@iitbmonash.org for more information on this, and other projects.